This Petition for Review from the May 28, 1993 Finding and Dismissal of the Commissioner acting for the Sixth District was heard June 10, 1994 before a Compensation Review Board panel consisting of the Commission Chairman Jesse M. Frankl and Commissioners Angelo L. dos Santos and Nancy A. Brouillet.

OPINION

JESSE M. FRANKL, CHAIRMAN. The claimant has petitioned for review from the May 28, 1993 Finding and Dismissal of the Commissioner acting for the Sixth District. He argues on appeal that the commissioner improperly concluded that the claimant’s employment did not aggravate or exacerbate his pre-existing disease. We affirm the trial commissioner’s decision.

The claimant, Michael Nihan, was employed at the respondent Bussman Industries from 1983 through the time that hearings in this case commenced. He claims that exposure to fumes, dust, materials and chemicals at his workplace caused an exacerbation or aggravation of his pre-existing condition known as sarcoidosis. Although the parties agree that the claimant suffers from that disease as an underlying nonoccupational condition, the respondents contested the work-relatedness of the worsening of the claimant’s disease.

After being referred to a specialist by his general practitioner, the claimant was diagnosed as having sarcoidosis by two physicians. The referred specialist opined that the claimant’s condition was exacerbated by his employment. The independent medical examiner who reviewed the claimant’s records and examined him testified that the claimant’s workplace had no involvement with the claimant’s condition, nor did it aggravate or exacerbate his symptoms. The commissioner accepted this testimony in concluding that the claimant had not established by a preponderance of the evidence that his sarcoidosis was in any way exacerbated by workplace conditions and dismissed the claimant’s claim. The claimant has appealed that decision.

This Board does not conduct a de novo review of the facts on appeal. Rather, the conclusions drawn by the trial commissioner from the facts found “must stand unless they result from an incorrect application of the law to the subordinate facts or from an inference illegally or unreasonably drawn from them.” Adzima v. UAC/Norden Division, 177 Conn. 107, 118 (1979). We cannot review the commissioner’s conclusions when they depend upon the credibility of the witnesses and the weight of the evidence. Id. “If supported by evidence and not inconsistent with the law, the [trial commissioner’s] inference that an injury did or did not arise out of and in the course of employment is conclusive.” Fair v. People’s Savings Bank, 207 Conn. 535, 539 (1988). This includes determinations pertaining to the work-relatedness of an occupational disease, Fritz v. Gravymaster, Inc., 12 Conn. Workers’ Comp. Rev. Op. 208, 209, 1462 CRB-3-92-7 (March 15, 1994); Biondi v. City of West Haven, 9 Conn. Workers’ Comp. Rev. Op. 203, 1024 CRD-3-90-5 (Sept. 3, 1991), where it is often necessary to rely upon expert medical opinion in determining causation. Metall v. Aluminum Co. of America, 154 Conn. 48, 52 (1966).

Here, the commissioner made a determination that the testimony of the respondents’ medical examiner was more persuasive than that of the claimant’s treating physician. It was within his discretion to decide which medical expert was more persuasive. As the testimony which the commissioner chose to credit supports his determination that the claimant’s pre-existing disease was not aggravated by his employment with the respondent, we cannot overturn his dismissal of the claimant’s claim.